How to select the varistor - Knowledge of electrical resistance

by:Thermistor-Mov     2020-06-21
How to select the varistor varistor is mainly introduced in this paper is how to choose, in this paper, probably about 1300 words, read the full article 13 minutes. Selects the piezoresistor before, should first understand the following relevant technical parameters: nominal voltage ( The pressure-sensitive voltage) Refers to the regulation of temperature, and the direct current flow, pressure sensitive resistor voltage value. Leakage current is refers to under the condition of 25 ℃, when the maximum continuous dc voltage source, through the current value of the pressure sensitive resistor. Level voltage is refers to the pressure sensitive resistance by 8/20 of a grade in the current pulse peak voltage present at both ends. Applying rules of pulse electric current (traffic is said 8/20μs) The peak current waveform. Surge environment parameters including the wave surge current Ipm ( Or the Vpm wave surge voltage and wave impedance Zo sites) , Tt surge pulse width, the smallest time interval of two adjacent surge Tm and the piezoresistor reservation period of working life, the total number of surge pulse N, etc. 1, nominal voltage selection generally, pressure sensitive resistor and often protected device or devices used in parallel, in normal circumstances, dc or ac voltage at the ends of the pressure sensitive resistor should be lower than nominal voltage, even in the worst power fluctuations, also should not be higher than the rating by selecting one of the biggest continuous working voltage, the maximum continuous working voltage corresponding to the nominal voltage value is chosen. For application of over-voltage protection, pressure-sensitive voltage value should be greater than the actual circuit of the voltage value, generally should be used to choose the type: VmA = av/BC type: a circuit for voltage fluctuation coefficient, typically take 1. 2; V work for circuit dc voltage ( When communicating to RMS) ; As to b for pressure-sensitive voltage error: 0. 85; As to c for component aging coefficient 0. 9. 414 times. In addition, also must pay attention to when choose: ( 1) Must ensure that the voltage fluctuation, the largest continuous working voltage will not exceed the maximum allowable values, otherwise will shorten the service life of the pressure sensitive resistance; ( 2) Between the power cord and the earth when using pressure sensitive resistance, sometimes due to the bad earth rising voltage between line and ground, and so often used is higher than line between line and occasions of piezoresistor of nominal voltage. 2, the selection of flux flow usually given product flow is given by product standard waveforms, impact time in testing the pulse frequency and clearance products can withstand the maximum current value. The product can withstand the impact of the number is a function of time waveform, amplitude and clearance, when the current waveform amplitude decreased 50% impact times can be doubled, so in practice, varistor absorption by the surge current flow should be less than the product of the chase. 3, the application is shown in figure 1 pressure-sensitive voltage device is adopted to surge and transient protection circuit connection diagram. For the application of pressure sensitive resistance connection, can be roughly divided into four types: the first type is between the power cord or the power cord and the earth connection, as pressure sensitive resistor, is the most representative application in the power cord and long distance transmission line lightning and make the wire such as surge pulse cases, protection of electronic products. General online indirectly into the piezoresistor on line between induction pulse effectively, while online and indirectly into the pressure sensitive resistance induction pulse effectively between the transmission line and the earth. If further connect the line to line and line to connect the two forms are combined, can has better absorption effect to surge pulse. The second type of load connected, it is mainly used for induction pulse caused by inductive load suddenly open and close to absorb, in order to prevent the damage to components. In general, just on the perceptual load in parallel, but according to the current type and energy of different size, can consider to share with R - C series absorption circuit. A third type is the contact between the connection, the connection is mainly to prevent induced charge switch contact arc burning, general parallel access and contact pressure sensitive resistor. The fourth type is mainly used for the protection of the semiconductor device connection, the connection mode is mainly used for thyristor, power transistor, such as semiconductor devices, generally USES and protection devices in parallel manner, to limit the voltage is lower than the stress levels of protection devices, it is a kind of effective protection for semiconductor devices. 文章/ ymdzdxy。 HTML this paper label: an article on resistance pressure sensitive resistance: the application of varistor type next article: what is the nominal pressure sensitive resistance parameters
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